Polyether, polyester and polyether ester purification process

ABSTRACT

A process is described for removing heteropoly compounds from heteropoly compound-contaminated polyethers, polyesters and/or polyether esters, which comprises admixing the polymer or a solution of the same with a compound which contains at least one heteroatom which is selected from the group consisting of central atoms of heteropolyacids, is non-protic and is of a polarity so low that its addition leads to the heteropoly compounds separating out in a separate phase, and separating off the precipitated heteropoly compound phase. The remaining polymer phase is preferably further purified using a solid adsorbent.

The invention relates to a process for purifying heteropolycompound-containing polyethers, polyesters and polyether esters or theirsolutions by mixing the same with a compound which contains at least oneheteroatom, which can be present as the central atom of a heteropolymercompound, is non-protic and is of a polarity so low that its additionleads to the separation of the heteropolymer compound in a separatephase.

Polyethers, polyesters and polyether esters are used in many ways;examples are their use in hydraulic oils or as diol component in thepreparation of polyurethanes. These compounds are prepared by cationicpolymerization or copolymerization of corresponding monomers, forexample cyclic ethers, acetates, polyalcohols or lactones, usingBronsted acid or Lewis acid catalysts. Heteropolyacids andheteropolyacid salts, jointly termed "heteropoly compound(s)" or "HPA"below, have proved to be particularly advantageous catalysts forring-opening polymerization. To establish the desired polymer molar massand/or to prepare special end-group-modified derivatives, substances arecustomarily present in the polymerization whose inclusion leads directlyor indirectly to chain termination. Examples of these are carboxylicacid derivatives, alcohols or water.

JP-A-33 028/1983 describes, for example, the polymerization oftetrahydrofuran (THF) in the presence of a carboxylic anhydride orcarboxylic acid halide with the formation of polyTHF diesters, aheteropolyacid being used as catalyst.

EP 126 471 teaches the HPA-catalyzed polymerization of THF and thecopolymerization of THF with various other cyclic ethers in the presenceof water, with the formation of poly(ether glycols). EP 158 229describes the preparation of poly(ether glycols) by copolymerization ofcyclic ethers with di- and higher-functional alcohols.

According to JP 61-200120, lactones, or lactones together with cyclicethers, can be polymerized in the presence of hydroxyl-containingcompounds with heteropolyacids as catalysts.

Poly(ether glycol)monoethers and poly(ether glycol)monoesters may beprepared according to EP 503 393 and EP 503 394 by polymerizing cyclicethers in the presence of monoalcohols or monocarboxylic acids with HPAcatalysts.

In these polymerization processes for preparing polyethers, polyestersand polyether esters, polymer phases are formed which, on account of theincomplete conversion, still contain residual amounts of monomer(s)residual amounts of the compound(s) leading to chain termination, anysolvents used, and also dissolved heteropoly compound(s). The percentageof HPA catalyst dissolved in the polymer phase is considerable in thesereactions and can be up to 1% by weight or more, based on the polymerphase. The dissolved catalyst does not precipitate out in the event of aseparation which merely consists of distilling off unreacted monomer,chain-termination reagent(s), and any solvent used, from this phase, butremains in dissolved form in the polymer. On the one hand, this must beprevented for quality reasons, and on the other hand it is desirable forreasons of costs, since heteropolyacids are very expensive, to recoverthe majority of the catalyst.

It is further known that heteropoly compounds decompose in the course oftime, more intensively under thermal stress. This occurs principally byhydrolysis, with formation of the corresponding oxides. Thedecomposition of heteropoly compounds can be decreased or completelyprevented if compounds are added which contain elements which can occuras central atoms in heteropoly compounds. For example, the hydrolyticstability of phosphorus poly acids is markedly increased in the presenceof phosphoric acid (A. Aoshima, S. Yamamatsu, T. Yamaguchi, NipponKagaku Kaishi, (1990) 233). The hydrolytic stability of HPA is likewiseincreased under reducing conditions (M. T. Pope, E. Papaconstantinou,Inorg. Chem. 6 (1967) 1147).

To solve the problem of separating off heteropoly compounds, it isproposed in EP 181 621 to add a hydrocarbon or halogenated hydrocarbonto the polymer phase, as a result of which the majority of the dissolvedheteropolyacid precipitates out and/or separates out as a separatephase. The separated hydrocarbon/polymer phase is then treated with asolid adsorbent. However, stabilization of the heteropoly compounds byprecipitation with a halogenated or non-halogenated hydrocarbon is notachieved in this process.

In SU 1754732 A1, after concentrating the polymer phase to 50-90%polymer, a hydrocarbon having 1-15 carbon atoms is likewise added toprecipitate out the heteropoly compound. However, instead of a furtherpurification by adsorption, a liquid organic nitrogen base is then addedwhich forms an insoluble salt with heteropoly compound still present,which must be the acid in this case, which salt precipitates out and canbe separated off in a conventional manner. However, the purity which canbe achieved in this manner of approximately 50×10⁻⁶ % heteropolycompound in the polymer is not adequate for most purposes.

It is an object of the present invention, therefore, to provide aprocess for purifying heteropoly compound-containing polyethers,polyesters and polyether esters or solutions of the same which canseparate off heteropoly compounds and at the same time can serve tostabilize the HPA used.

We have found that this object is achieved by a process for removingheteropoly compounds from heteropoly compound-contaminated polyethers,polyesters and/or polyether esters, which comprises mixing thesepolymers or a solution of the same with a compound which contains atleast one heteroelement which is selected from the group consisting ofcentral atoms of heteropolyacids, is non-protic and is of a polarity solow that its addition leads to the precipitation of the heteropolycompound.

Polyethers, polyesters and/or polyether esters can be freed fromheteropoly compound(s) by the process according to the invention.

The purification process described can be used for any mixture whichcomprises HPA and polymers of this type.

Said polymeric compounds can, for example, be made up of monomers of thegroup consisting of the cyclic ethers, acetals, diols, higher alcoholsand lactones. However, it is also possible to free polymeric compoundscomprising other monomers from dissolved heteropoly compounds by theprocess according to the invention. The molar mass of the polyethers,polyesters and/or polyether esters to be purified is not restricted, butis preferably below 5000.

The polyethers, polyesters and/or polyether esters containing theheteropoly compound(s) are used as such or in dissolved form, forexample and preferably in their solution arising in the polymerization.In this description and in the claims, a phase which contains at leastone of the above polymers is termed "polymer phase" or "(polymer)mixture", whereas a phase which additionally contains a low-molecularweight organic component acting as solvent is termed a "polymersolution".

The polymerization process itself is not of particular importance forthe purification according to the invention of polyethers, polyestersand/or polyether esters. The polymerization can be carried outcontinuously or batchwise and the polymerization system can be, forexample, single-phase, two-phase or heterogeneous.

Generally, the polymer solution formed in the polymerization stillcontains a considerable proportion of monomer(s), a large amount of thechain termination reagent(s) initially added and dissolved heteropolycompound(s). Since it can be advantageous to carry out thepolymerization in the presence of a solvent, the polymerization systemmay also contain such a solvent.

In a preferred polymerization process using HPA catalysis, the procedureis carried out in such a manner that a polymerization mixture having twoliquid phases is formed, the one phase being the catalyst phase and theother being the monomer/polymer phase. A typical monomer/polymer phaseas formed, for example, in the ring-opening polymerization of THF togive polytetrahydrofuran (PolyTHF) in the presence of water using H₃PW₁₂ O₄₀ as catalyst in a two-phase polymerization system, has thefollowing composition (figures in % by weight): 77.3% THF, 21.2%PolyTHF, 1.2% H₃ PW₁₂ O₄₀, 0.3% water.

The composition of the polymer phase which is used for the processaccording to the invention accordingly depends on the type of thecatalyst, the monomer or monomers, the chain termination reagent(s) andon the content of solvent which may have been used and is not criticalfor the process.

According to the novel process, to purify the HPA-containing polymers,compounds are added which contain at least one heteroatom which canoccur as central atom in heteropoly compounds, are non-protic and are ofa polarity so low that their addition leads to the precipitation of thedissolved heteropoly compound(s).

For the purposes of the present invention, heteropolyacids are inorganicpoly acids which have at least two different central atoms and areformed as mixed, partial anhydrides from weak, polybasic oxygen acids ofa metal, preferably from those of chromium, molybdenum, vanadium andtungsten, and/or the corresponding oxides of these metals, for exampleCrO₃, MoO₃, V₂ O₅ or WO₃, and those of another metal or nonmetal, forexample arsenic, boron, iodine, phosphorus, selenium, silicon,germanium, or tellurium. Generally, the atomic ratio of the former tothe latter elements in these heteropolyacids is from 2.5 to 12,preferably 9 or 12.

Examples of heteropolyacids which can be removed from the processaccording to the invention are the following compounds:

dodecamolybdatophosphoric acid (H₃ PM₁₂ O₄₀ ·nH₂ O),

dodecamolybdatosilicic acid (H₄ SiMo₁₂ O₄₀ ·nH₂ O),

dodecamolybdatoceric(IV) acid (H₈ CeMo₁₂ O₄₀ ·nH₂ O),

dodecamolybdatoarsenic(V) acid (H₃ AsMo₁₂ O₄₀ ·nH₂ O),

hexamolybdatochromic(III) acid (H₃ CrMo₆ O₂₄ H₆ ·nH₂ O),

hexamolybdatonickelic(II) acid (H₄ NiMo₆ O₂₄ H₆ ·5H₂ O),

hexamolybdatoiodic acid (H₅ IMo₆ O₂₄ ·nH₂ O),

octadecamolybdatodiphosphoric acid (H₆ P₂ Mo₁₈ O₆₂ ·11H₂ O),

octadecamolybdatodiarsenic(V) acid (H₆ As₂ Mo₁₈ O₆₂ ·25H₂ O),

nonamolybdatomanganic(IV) acid (H₆ MnMo₉ O₃₂ ·nH₂ O),

undecamolybdatovanadatophosphoric acid (H₄ PMo₁₁ VO₄₀ ·nH₂ O),

decamolybdatodivanadatophosphoric acid (H₅ PMo₁₀ V₂ O₄₀ ·nH₂ O),

dodecavanadatophosphoric acid (H₇ PV₁₂ O₃₆ ·nH₂ O),

dodecatungstosilicic acid (H₄ SiW₁₂ O₄₀ ·7H₂ O),

dodecatungstophosphoric acid (H₃ PW₁₂ O₄₀ ·nH₂ O),

dodecatungstoboric acid (H₅ BW₁₂ O₄₀ ·nH₂ O),

octadecotungstodiphosporic acid (H₆ P₂ W₁₈ O₆₂ ·14H₂ O),

octadecotungstodiarsenic(V) acid (H₆ As₂ W₁₈ O₆₂ ·14H₂ O),

hexamolybdatohexatungstophosphoric acid (H₃ PMo₆ W₆ O₄₀ ·nH₂ O).

Obviously, mixtures of heteropolyacids can also be removed. Frequently,the process according to the invention serves to removedodecotungstophosphoric acid, dodecotungstosilicic acid and/ordodecomolybdatosilicic acid, since these are preferentially used ascatalysts owing to their ready availability.

The process according to the invention is particularly preferably usedfor the purification of polymers in whose preparation processes the freeheteropolyacids have been used as catalysts. However, it is alsopossible to separate off alkaline metal salts and/or alkaline earthmetal salts of heteropolyacids.

The heteroatoms of the compound as described in claim 1 used to removeheteropoly compounds can therefore be main group and subgroup elementsof the Periodic Table of the Elements. Examples of main groupheteroelements are boron, silicon, germanium, tin, phosphorus, arsenic,antimony, selenium and tellurium. Examples of subgroup heteroelementsare cerium, vanadium, chromium, molybdenum, tungsten, manganese andnickel.

For the purposes of this invention, "non-protic" is a compound whosepKa≧20.

By choosing suitable substituents, the compound serving for HPAprecipitation can be optimally matched to the polymer to be purified orits solution. Furthermore, for an additional increase in the hydrolyticstability, compounds are preferred which have a reducing action, i.e.they can themselves be oxidized. These are compounds in which theheteroelement is not present in the highest oxidation state. Examples ofheteroelement compounds used in the process according to the inventionare: phosphites, such as triethyl phosphite, phosphonates, such asdimethyl methanephosphonate, phosphines, such as tributyl phosphine,phosphine oxides, such as tributylphosphine oxide, silanes, such astetramethylsilane, triisopropylchlorosilane, methoxytrimethylsilane ortetrabutoxysilane, heteroelement-containing ethers, such asbis(trimethylsilyl) ether, boranes, such as trisborane, or tetraalkyltincompounds, such as tetrabutyltin.

The heteroelements present in these compounds are preferably those whichare present in the respective HPA catalysts used, e.g. phosphorus intriethyl phosphite as heteroelement compound used for the precipitationand in dodecamolybdatophosphoric acid as catalyst. However, compoundswhose heteroelement differs from that in the HPA employed can also beused, for example silicon in tetramethylsilane as heteroelement compoundemployed for the precipitation, with dodecatungstophosphoric acid usedas catalyst.

To simplify the process according to the invention, heteroelementcompounds which are liquid at room temperature are preferably used forthe precipitation. Furthermore, the heteroelement compounds shouldadvantageously be stable under the reaction conditions.

The amount by weight of the heteroelement compound to be used depends onthe HPA content and on the content of other low-molecular weightcompounds, such as monomer(s), chain termination reagent(s), solvent(s)etc. in the polymer phase to be purified, but is usually at least halfas much as, frequently as much as up to twice as much as the totalamount by weight of the other low-molecular weight compounds. Based onthe amount of polyether, polyester and/or polyether ester, the amount ofheteroelement compound should generally be 50% by weight or more,preferably 100% by weight or more.

If large amounts of low-molecular weight compounds are present togetherwith the polymer to be purified, large amounts of heteroelement compoundwould also have to be added to precipitate the HPA. It can therefore beexpedient to concentrate a polymer-containing mixture to a polymercontent of at least 10, or preferably at least 50, % by weight or more,prior to addition of the heteroelement compound employed forprecipitation.

With the addition according to the invention of the heteroelementcompound, the majority of the HPA dissolved in the polymer phaseprecipitates out. It can be advantageous here to mix the polymer phasein a suitable manner, for example by conventional stirring. Temperaturesand pressures at which the process can be carried out simply are chosenfor the HPA removal. The temperatures employed should not be too high,since the HPA solubility in the polymer phase increases with increasingtemperature; usually, temperatures from 25° to 60° C. are chosen. Themixture can stand from 0.1 to 200 hours to complete the precipitation,0.5 hours usually being sufficient. The formation of emulsions isfrequently observed. In this case, the phase separation can beaccelerated by suitable measures (e.g. use of a coalescing filter).

The majority of the HPA dissolved in the polyether, polyester arid/orpolyether ester phase is successfully separated off by means of theprocess according to the invention. The HPA usually arises in the liquidphase, which can be recycled directly to the polymerization stage.

If, for example, the abovementioned THF/polyTHF phase, which is obtainedin the THF polymerization in the presence of water and H₃ PW₁₂ O₄₀ ascatalyst, is admixed with half the amount by weight oftetramethylsilane, the majority of the dissolved HPA separates out inthe form of a liquid phase. The residual HPA content in theTHF/polyTHF/tetramethylsilane phase decreases to 5 ppm here.

The processes proceeding in the precipitation of HPA by addition of theheteroelement compound have not yet been clarified in all details. Apossible mechanism could be that the addition of the heteroatomiccomponent greatly decreases the solubility of heteropoly compounds inthe polymer phase by decreasing the polarity of same, so that theyprecipitate out from the polymer phase.

Polyethers, polyesters and polyether esters having an HPA contentdecreased as described above can be further purified by contacting themwith a solid adsorbent, directly or in solution. Preference is given tothe use of monomer/polymer mixtures which may still contain solvent.These mixtures can be used in the form in which they arise in HPAprecipitation, or else in concentrated or dilute form. The amount ofmonomer advantageously present in the polymer phase should be at least10% by weight, better 50% by weight or more.

The type of solid adsorbent is not restricted, provided that it canadsorb heteropoly compounds. Preference is given to activated carbons,aluminum oxides, oxides, hydroxides and carbonates of alkaline earthmetals and rare earth metals and basic ion exchangers. The amount ofadsorbent depends on the HPA content and can be 2 to 5000 times,preferably 10 to 1000 times, that of dissolved HPA. Generally, the useof larger amounts of solid adsorbent leads to a lower residual HPAcontent after the treatment.

The temperature in this purification step is not particularly restrictedand should be selected in such a manner that the solution to be treatedhas a suitable viscosity. If a polyether having a mean molar mass of1000 is used in pure form, the suitable temperature is usually from 20°to 150° C., preferably from 30° to 100° C.

If, after the treatment with a solid adsorbent, the purified polymerstill contains monomer or solvent, they may be removed, for example, bydistillation at atmospheric pressure or under reduced pressure, in whichcase a polymer having a very low HPA content can be obtained, which canbe below 1 ppm, based on pure polyether, polyester and/or polyetherester. Therefore, polyethers, polyesters and/or polyether esters can beobtained in high purity in an economical manner by the process accordingto the invention.

The examples below illustrate the invention; all percentages forconcentrations are by weight. The experiments were all performed undernitrogen. The heteropolyacids were quantitatively analyzed by x-rayfluorescence and atomic absorption.

EXAMPLE 1

A polymer phase was used which arose in the polymerization oftetrahydrofuran (THF) to give polytetrahydrofuran (polyTHF) in thepresence of water using H₃ PW₁₂ O₄₀ as catalyst, and had the followingcomposition: THF (77.3%), polyTHF (21.2%), H₃ PW₁₂ O₄₀ (1.2%), water(0.3%).

100 g of this mixture were admixed with 200 g of triethyl phosphite.After 30 hours, the majority of the previously dissolved H₃ PW₁₂ O₄₀ hadprecipitated out in the form of a liquid mixture and could be separatedoff. The THF/polyTHF/triethyl phosphite phase still had a residualcontent of 200 ppm of H₃ PW₁₂ O₄₀. The organic phase was then admixedwith 20 g of activated carbon (Merck) and was shaken for 4 hours at roomtemperature. In the polyTHF which was obtained after separating off theactivated carbon and concentration under reduced pressure, the H₃ PW₁₂O₄₀ content was in all cases below 1 ppm.

EXAMPLE 2

A polymer phase was used, which arose in the polymerization ofcaprolactone to give polycaprolactone in the presence of water using H₃PW₁₂ O₄₀ as catalyst, and had the following composition:polycaprolactone (98.2%), H₃ PW₁₂ O₄₀ (1.8%). 100 g of this mixture wereadmixed with 200 g of triethyl phosphite. After 30 hours, the majorityof the previously dissolved H₃ PW₁₂ O₄₀ had precipitated out in the formof a liquid mixture and was separated off. TheTHF/polycaprolactone/triethyl phosphite phase still had a residualcontent of 420 ppm of H₃ PW₁₂ O₄₀. The organic phase was then admixedwith 20 g of activated carbon (Merck) and shaken for 4 hours at roomtemperature. The H₃ PW₁₂ O₄₀ content in the polycaprolactone obtainedafter separating off the activated carbon and concentration underreduced pressure was below 1 ppm.

EXAMPLES 3-11

In each of Examples 3-11, 100 g of a THF/polyTHF/HPA solution whosecomposition is specified in Table I was used. The heteroatom-containingcompound indicated as "purification compound" was added to this mixtureand the residual HPA content in the mixture was determined after 50hours. All samples were then admixed with 20 g of activated carbon,shaken for 4 hours at room temperature and then concentrated at 10mbar/140° C. Analysis of the polyTHF thus obtained gave a residual HPAcontent of less than 1 ppm.

                  TABLE I                                                         ______________________________________                                        Composition of the                                                            solution                       Residual                                               poly-       Purification compound                                                                        HPA                                        THF       THF    HPA             Amount                                                                              content                                Example                                                                               % by weight!                                                                              Type        g!    ppm!                                    ______________________________________                                        3      77.3   21.2   1.2  tetramethyl-                                                                           50    5                                                              silane                                              4      77.3   21.2   1.2  tetraethylsilane                                                                       50    5                                    5      77.3   21.2   1.2  tetrabutyltin                                                                          50    5                                    6      77.3   21.2   1.2  tetrabutoxy-                                                                           50    5                                                              silane                                              7      77.3   21.2   1.2  trisdimethyl-                                                                          50    5                                                              aminoborane                                         8      77.3   21.2   1.2  dimethyl 50    5                                                              methanephos-                                                                  phonite                                             9      77.3   21.2   1.2  tributyl-                                                                              50    5                                                              phosphine                                                                     oxide                                               10     77.3   21.2   1.2  triisopropyl-                                                                          50    5                                                              chlorosilane                                        11     77.3   21.2   1.2  bis(tri- 200   8                                                              methylsilyl)                                                                  ether                                               ______________________________________                                    

We claim:
 1. A process for removing heteropoly compounds from heteropolycompound-contaminated polyethers, polyesters or polyether esters, whichcomprises admixing the polymer or a solution of the polymer with acompound which contains at least one heteroatom which is selected fromthe group consisting of central atoms of heteropolyacids, is non-proticand is of a polarity that leads to the heteropoly compounds separatingout in a separate phase, and separating off the precipitated heteropolycompound phase.
 2. A process as defined in claim 1, wherein theheteroatom in the compound containing at least one heteroatom isselected from the group consisting of B, Si, Ge, Sn, P, As, Sb, Se, Te,Ce, V, Cr, Mo, W, Mn and Ni.
 3. A process as defined in claim 2, whereinthe heteroatom is selected from the group consisting of B, Si or P.
 4. Aprocess as defined in claim 1, wherein the compound containing at leastone heteroatom is not present in its highest oxidation state.
 5. Aprocess as defined in claim 1, wherein an amount by weight of thecompound containing at least one heteroatom is added which is at leasthalf as much as the amount by weight of other low-molecular weightcompounds present or is at least 50% of the amount by weight of polymerpresent.
 6. A process as defined in claim 1, wherein a solution of thepolymer is concentrated to a polymer content of at least 10% by weight,preferably at least 50% by weight, before it is admixed with thecompound containing at least one heteroatom.
 7. A process as defined inclaim 1, wherein, after separating off the heteropoly compound phase,the polymer is contacted with a solid adsorbent which is capable ofadsorbing heteropoly compounds.
 8. A process as defined in claim 1,wherein the solid adsorbent used is one, or a mixture of a plurality,selected from the group consisting of activated carbons, aluminumoxides, alkaline earth metal oxides and rare earth metal oxides,hydroxides and carbonates and basic ion exchangers.
 9. A process asdefined in claim 1, wherein, after removing the heteropoly compounds,the polymer is obtained by separating off monomers, chain terminationreagents, any solvents added and other low-boiling compounds.
 10. Aprocess as defined in claim 1, wherein a polyether containingpolyoxytetramethylene groups is used.
 11. A process as defined in claim1, wherein the heteropoly compound phase separated off is reused aspolymerization catalyst.
 12. The process as defined in claim 6, whereinthe polymer content is at least 50% by weight.